1. Field of the Invention
The present invention relates to a fuel cell system.
2. Description of the Related Art
Recently, there have been rapidly progressed various developments of fuel cells that generate power by supply with hydrogen (fuel gas) and oxygen (oxidant gas); for example, fuel cells are increasingly applied to a fuel cell vehicle as its power source. Such fuel cells include an anode flow passage (fuel gas flow passage) and a cathode flow passage (oxidant gas flow passage) therein.
However, while power generation in fuel cells is stopped, that is, in a state in which fuel cells are electrically disconnected to an external load, when air externally flows into the cathode flow passage and this air (oxygen) is consumed by an electrode reaction under a cathode catalyst (such as Pt, Ru), so that potential of the cathode may increase, or residual moisture may be discomposed, consequently generating high-activated OH radical, etc. Such an increase of the cathode potential or generation of OH radical, etc. may cause oxidation of carbon (C) of carbon paper constituting the cathode and the catalyst, or decomposition of electrolyte membrane, resulting in deterioration of the fuel cells.
Some of the air flown in the cathode flow passage passes through the electrolyte membrane so that there cross-leak of the air to the anode occurs, and if this cross-leaked air is consumed under the anode catalyst, potential of the anode may increase or OH radical, etc., may be generated, so that carbon (C) of carbon paper constituting the cathode and the catalyst may be oxidized, or decomposition of electrolyte membrane may be caused, resulting in deterioration of the fuel cells.
To address such a problem, there has been proposed a fuel cell system in which normally closed type electromagnetic valves, each of which incorporates a solenoid, are provided in upper and lower reaches of the cathode, respectively; while power generation in the fuel cells is stopped, the electromagnetic valves are closed to block the cathode flow passage so as to prevent a fresh air flow externally flowing into the cathode flow passage, thereby to reduce cross leak amount of the air from the cathode to the anode (see JP 2006-221836 A).
However, the fuel cell system, as disclosed in JP 2006-221836 A, includes the normally closed type electromagnetic valves at the upper and lower reaches of the cathode flow passage, and while the air is being flown through the cathode flow passage in order to generate power in the fuel cells, current is needed to be continuously supplied for the solenoids of the electromagnetic valves to maintain the electromagnetic valves in the open state. Specifically, while maintaining the electromagnetic valve in the open state, power generated by the fuel cells and power stored in a battery are being consumed at the solenoids, resulting in inefficiency of power generation.
The present invention has an object to provide a fuel cell system that blocks an oxidant gas flow passage, as well as reducing consumption of energy such as electric power.